1. Field of the Invention
The invention generally relates to network communications, and, in particular, to a method and apparatus for multicast tunneling for mobile devices.
2. Description of the Related Art
Mobile IPv6 (MIPv6) is a protocol developed as a subset of Internet Protocol version 6 (IPv6) to support mobile connections. MIPv6 is an update of the IETF (Internet Engineering Task Force) Mobile IP standard (RFC 2002) designed to communicate with mobile devices (known as mobile nodes) using IPv6 addresses.
In traditional IP routing, IP addresses represent a topology. Routing mechanisms rely on the assumption that each network node will always have the same point of attachment to the Internet, and that each node's IP address identifies the network link where it is connected. In this routing scheme, a person desiring to disconnect a mobile device from the Internet and then to reconnect it through a different network would have to configure the device with a new IP address, the appropriate netmask, and default router. Otherwise, routing protocols may not have a means of delivering datagrams (packets), because the device's network address does not contain the necessary information about the node's network point of attachment to the Internet.
MIPv6 allows a mobile node to transparently maintain connections while moving from one subnet to another. Each device is identified by its home address although it may be connecting through another network. When connecting through a foreign network, a mobile device sends its location information to a home agent. The home agent intercepts packets that are intended for the mobile node and tunnels them to the mobile node's current location. The mobile node also typically informs the correspondent node about its new location, so that only the first few packets are tunneled through the home agent.
MIPv6 specifies that multicast packets addressed with a global scope to which the mobile node has successfully subscribed must be tunneled to the mobile node. Because multicast packets are addressed to a group of hosts, these packets are tunneled through the home agent—that is, the correspondent node does not learn about the possible new locations of every member of the group. As such, the home agent must separately tunnel multicast packets for each of the mobile nodes to their new location. This, however, can be inefficient, giving rise to network traffic, particularly if a large number of network nodes move to a foreign network. Moreover, if the network nodes happen to move to a common part of a network, the home agent will transmit multiple packets to those nodes in the same direction, thereby possibly congesting the network path.
The present invention is directed to addressing, or at least reducing, the effects of, one or more of the problems set forth above.